Hydrogen peroxide solutions have been used for many years for a variety of purposes, including bleaching, disinfecting, and cleaning a variety of things and surfaces ranging from skin, hair, and mucous membranes to contact lenses to household and industrial surfaces and instruments. In particular, peroxide-containing bleaching agents have long been used in washing and cleaning processes. When soiled clothing is contacted with such bleaching compositions, usually by washing the soiled clothing in the presence of the bleaching composition at the boil, the bleaching agent functions to remove such common domestic stains as tea, coffee, fruit and wine stains from clothing.
Traditionally, to clean a substrate such as clothing, the substrate is subjected to hydrogen peroxide, or to substances which can generate hydroperoxyl radicals, such as inorganic or organic peroxides. Generally, these peroxide systems must be activated in order to work properly. One method of activating the system is to employ wash temperatures of 60° C. or higher, but it is often advantageous to wash laundry in cold water (e.g., temperatures from about 2-24° C.). Washing in cold water generally conserves energy and therefore costs less money than washing in warm water. Other advantages include potentially less damage to clothes. However, if the washing temperature is reduced to below 60° C., the efficacy of the peroxides in the bleaching agent is correspondingly reduced.
In order to avoid having to employ wash temperatures of 60° C. or higher, it is well-known that certain heavy metals, or complexes thereof, function to catalyze the decomposition of hydrogen peroxide, or of compounds which are capable of liberating hydrogen peroxide, in order to render the peroxide compound effective at temperatures below 60° C. Various transition metal ions added in the form of suitable salts, and coordination compounds containing such cations, are known to activate hydrogen peroxide (H2O2). In that manner, by using certain heavy metals as catalysts, it is possible for the bleaching effect (which is unsatisfactory at lower temperatures) of H2O2, or precursors that release H2O2 and of other peroxo compounds, to be increased.
In terms of H2O2 activation having effective bleaching action, mononuclear and polynuclear variants of manganese complexes having various ligands, especially 1,4,7-trimethyl-1,4,7-triazacyclononane and optionally oxygen-containing bridging ligands, are currently regarded as being especially effective. Such catalysts are adequately stable under practical conditions and, with Mnn+, contain an ecologically acceptable metal cation, but their use is unfortunately associated with considerable damage to dyes and fibres.
For example, in U.S. Pat. No. 5,114,511, there is described the activation of a peroxy compound by a complex formed from a transition metal (Mn, Co, Fe or Cu) and a non-(macro)cyclic ligand, preferably 2,2-bispyridylamine or 2,2-bispyridylmethane.
Moreover, in U.S. Pat. No. 5,114,606, there is disclosed a manganese complex, for use as a bleach catalyst for a peroxy compound, which is a water-soluble complex of manganese II, III or IV, or mixtures thereof, with a ligand which is a non-carboxylate polyhydroxy compound, having at least three consecutive C—OH groups in its molecular structure, preferably sorbitol.
The incorporation of some ingredients into detergent compositions is problematic. Detergent compositions are often stored for some time and interactions may occur between active components such that a reduction in the amount of the active component may result. This can be particularly problematic in the presence of moisture.
Many ways of protecting and delivering sensitive, highly active, low dosage detergent components have been suggested. In EP-A-0072166, EP-A-0124341, EP-A-224952 and WO 95/06710, heavy metal complexes are incorporated into detergent compositions in agglomerated or aggregate form in order to improve storage stability. In EP-A-170346, bleach catalysts are adsorbed onto solid silicon supports. In EP-A-141 470, heavy metal ion catalysts are protected by selecting specific ligands and then providing a protective coating; in EP-A-141472, micronised coatings are described. In EP-A-544 440, gelled polymers are used; in WO 95/33817, wax encapsulation is used requiring a surfactant in the particle. Unfortunately, coating methods are costly and coated/encapsulated particles are vulnerable to fissures or incomplete coatings leading to loss of the active component(s) in the particle.
Problems arise in the addition to the formulation or incorporation of a bleaching (agent) components when the composition is a liquid, particularly aqueous washing and cleaning agents that are enjoying an increased popularity due to their positive product properties, such as a better and faster solubility and practicality. Due to the decomposition reactions or hydrolysis and incompatibilities towards other constituents of the washing agent formulation, such as, e.g., enzymes or surfactants, the added bleaching agents often lose their activity already on storage or even during product utilization. An adverse consequence resulting from this is that the washing performance—particularly the bleaching power—of the washing agent formulation noticeably deteriorates, such that bleachable stains in particular can no longer be satisfactorily removed.
Bleaching agents, such as for example perborates or percarbonates, which are usually used in solid washing agent formulations, are extremely moisture sensitive, with the result that they often lose their bleaching power within a few days in a liquid and particularly aqueous washing or cleaning agents, due to the loss of active oxygen.
Decomposition of hydrogen peroxide caused by catalytically active substances, such as metal ions, is extremely difficult to prevent. For products that contain hydrogen peroxide to be effective, a substantial proportion of the hydrogen peroxide must survive between manufacture and use. In addition, decomposition produces oxygen gas, which could overpressure the container and cause it to rupture during storage or shipping. Examples of such compositions are given, for example, in Kott, U.S. Pat. No. 5,641,739; Scialla, U.S. Pat. No. 5,559,090; Monticello, U.S. Pat. No. 6,106,774; and Kandathil, U.S. Pat. No. 4,238,192.
Liquid detergent compositions offer several advantages over solid compositions. For example, liquid compositions are easier to measure and dispense. Additionally, liquid compositions are especially useful for direct application to heavily soiled areas on fabrics, after which the pre-treated fabrics can be placed in an aqueous bath for laundering in the ordinary manner.
Unfortunately, unless very stringent conditions are met, hydrogen peroxide solutions begin to decompose into O2 gas and water within an extremely short time. Typical hydrogen peroxide solutions in use for these purposes are in the range of from about 0.5 to about 6% by weight of hydrogen peroxide in water. The rate at which such dilute hydrogen peroxide solutions decompose will, of course, be dependent upon such factors as pH and the presence of trace amounts of various metal impurities, such as copper or chromium, which may act to catalytically decompose the same. Moreover, at moderately elevated temperatures, the rate of decomposition of such dilute aqueous hydrogen peroxide solutions is greatly accelerated. Hence, hydrogen peroxide solutions which have been stabilized against peroxide breakdown are in very great demand.